Rotax 914 with CS prop

Hi, 

914 with Constant Speed prop

I wonder if anyone else has found this problem with constant speed props on a Rotax 914.

Using Rotax 914 manual recommended MP pressure and revs chart, this problem occurred with both an hydraulic and electric CS prop

1.       Take off; I find that on full fine prop pitch and take off power the engine is very smooth in the climb – fine, no problem.

2.       Transition to max continuous power;  i.e.  first reduce power to selected MP then increase prop pitch to matching recommended revs and the engine is still smooth.

3.       Transition to lower speed cruise; I then first reduce power to selected MP then increase prop pitch to matching recommended revs and the engine is still smooth.

4.       BUT if I increase the cruise speed;  i.e. first reduce prop pitch to selected higher revs and increase power  to matching MP, there is a small but definite vibration similar to being in too high gear in a car.    This vibration remains even at reduced or increased power settings, and only “resets” when landed and take off again.